voltage drop distances

[shawn73]

I am installing 20A 120V recepticles in our factory. The run from the main 208/120V panel is approx. 300 foot from the farthest outlet. This is the longest run I've ever installed. Should I over-rate the wire to compensate for voltage drop? At what distance should I be concerned with such issues? Thanks for the help.

[ August 22, 2005, 09:24 AM: Message edited by: shawn73 ]

 

[augie47]

Re: voltage drop distances

If my handy-dandy calculator hasn't failed me...
To maintain a 3% voltage drop you would need to run a #3 (at a 20 amp load), at a 16 amp load, #4

 

[lizzie14]

Re: voltage drop distances

Be sure to upsize the equipment ground accordingly if you change your wire size based on voltage drop.

 

[Duuuuug]

Re: voltage drop distances

Try this link, but all web calculators have disclaimers.
http://www.electrician.com/vd_calculator.html

 

[LarryFine]

Re: voltage drop distances

Shawn, this sounds like a perfect job for a sub-panel (or two). A feeder sized for a few circuits will exhibit much lower voltage drop over this distance than will individual circuits.

To use Augie's numbers, it would be much more economical to make a single 300' run using the same #3 copper w/100-a breaker, and branch out from a point central to the receptacle locations.

We're just finishing up a big (7500+ sq.ft. - basement over 3000!) house with two 200-a panels (one on standby gen), and I ran two 100-a sub-panels (one on each panel) to the far end of the house.

Addendum: Note: for a 300' run, a 100-a panel will require larger than #3, unless you'll rarely use more than one circuit per phase to capacity at any given moment.

[ August 22, 2005, 07:42 PM: Message edited by: LarryFine ]